Spectrophotometric analysis is commonly applied to many liquids to determine the contents. Such analysis is particularly useful if done with near infrared radiation, due to the latter's ability to discriminate between a target analyte and other substances.
That such analysis is possible to ascertain hemoglobin, glucose, albumin, lipids, and many other sera components is evident from, e.g., Clin. Chem., Volume 38, Pages 1623-1631 (1992).
Problems have existed, however, in applying such analysis to blood samples to determine the contents or quality of such samples. It has been difficult, for example, to apply it to samples as they are obtained initially, namely in primary patient collection containers. These are usually tubes of varying size that have been centrifuged to separate the liquid serum or plasma from the cellular phases. Such tubes therefore have a) a patient-identification label, b) varying and unpredictable locations of the sera to be analyzed, and c) a large amount (milliliters) of sample required. As to the varying locations, the gel barrier used to separate the liquid phase from the cellular phase, if scanned instead of the liquid phase, no doubt will produce an incorrect evaluation.
Thus, it has been the practice, when dealing with tubes of liquid of unpredictable height, to aliquot into a secondary tube, with added exposure and time, or ascertain where the liquid phase is, such as by LED scanning of the tube contents, as shown, for example, in FIG. 3 of EPA 185,330. Such requirements introduce additional equipment expenses and process delays. This, coupled with the difficulties of spectrophotometrically scanning through the patient label, has rendered such scanning of primary collection containers problematic and expensive.
On the other hand, conventional clinical analyzers using dried slide test elements to test for target substances, require usually at least five minutes to conduct an assay of the target substance, given the need for incubation. With these incubator times, it becomes difficult to obtain throughputs much greater than about 1000 tests per hour. A technique that would allow for much higher throughput in such analyzers is sorely needed.
Thus, there has existed prior to this invention, the need to provide an inexpensive and simple method of spectrophotometric scanning of biological liquids such as blood sera or plasma separated from whole blood, that is, one which eliminates the need to locate the liquid's position in whatever container is used, and the need to scan through an identification label. There is further a need to enhance the throughput of tests in an analyzer that assay target substances.